Medical devices to be inserted in vivo, such as catheters, guidewires, and indwelling needles, are required to have excellent lubricity in order to reduce tissue damage in blood vessels or the like and also improve the operability for the operator. For this reason, methods for forming a coating of a hydrophilic polymer having lubricity on a surface of a base layer have been developed, and put into practical use. In such a medical device the elution and separation of the hydrophilic polymer from the base layer surface is problematic in terms of maintaining the safety and operability. For this reason, a coating of a hydrophilic polymer is required to have not only excellent lubricity but also durability against loads such as abrasion and scratching.
From such a point of view, Japanese Patent No. JP-A-8-33704 discloses a medical device, which is obtained by dissolving a water-soluble or water-swellable polymer in a solvent that swells a base material of a medical device to produce a polymer solution, immersing a base material of a medical device in the polymer solution to cause swelling, and further crosslinking or polymerizing the polymer on the base material surface, thereby forming a surface lubrication layer on the base material surface.
According to the technique disclosed in Japanese Patent No JP-A-8-33704, a surface lubrication layer having relatively good lubricity can be fixed to a base material.
Japanese Patent No. JP-A-8-33704 discloses that it is preferable to use a block copolymer having a hydrophilic portion that exhibits lubricity and a portion that has an epoxy group for the water-soluble or water-swellable polymer. Further, when such a block copolymer is used, epoxy groups can be crosslinked by a heating operation, whereby a surface lubrication layer that is relatively hard to separate can be formed. However, there is a trade-off relationship between good lubricity and excellent durability, and thus a technique to achieve good lubricity and excellent durability at the same time has been demanded.
In particular, in recent years, medical devices have been made significantly smaller and thinner, and a medical procedure in which a medical device approaches a winding and narrower lesion in vivo has been gaining in popularity. Accordingly, in order to maintain good device operability even in a complicated lesion, there has been a demand for a technique to provide the surface of a device with higher lubricity and durability than before.
Therefore, there has been a demand for a technique to improve both lubricity and durability at the same time so as to support medical procedures that are becoming more complicated and advanced.